Defrost refrigeration system

ABSTRACT

A defrost refrigeration system comprises first compressors and second compressors serially positioned with respect to one another such that refrigerant going through a compression stage in the refrigeration cycle passes sequentially through the first compressors and the second compressors. A first line extends from an exit of one of the first compressor and the second compressor of the compression stage, and is in fluid communication with the evaporator stage in a defrost cycle and is adapted to receive a defrost portion of refrigerant compressed in the compression stage. Valves switch evaporators between the refrigeration cycle and the defrost cycle, by stopping/allowing a flow of refrigerant from the condensation stage to the evaporators of the evaporation stage in the refrigeration cycle, and for allowing/stopping a flow of said defrost portion of refrigerant to defrost the evaporators in the defrost cycle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to refrigeration systems, and more particularly to defrost configurations for evaporators of industrial and commercial refrigeration cabinets, by which hot refrigerant is circulated in the evaporators for defrost.

2. Background Art

In refrigeration systems found in the food industry to refrigerate fresh and frozen foods, it is necessary to defrost the refrigeration coils of the evaporators periodically, as the refrigeration systems working below the freezing point of water are gradually covered by a layer of frost which reduces the efficiency of evaporators. The evaporators become clogged up by the build-up of ice thereon during the refrigeration cycle, whereby the passage of air maintaining the foodstuff refrigerated is obstructed. Exposing foodstuff to warm temperatures during long defrost cycles may have adverse effects on their freshness and quality.

According to a method known in the art, gas is taken from the top of the reservoir of refrigerant at a temperature ranging from 80° F. to 90° F. and is passed through the refrigeration coils, whereby the latent heat of the gas is used to defrost the refrigeration coils. This also results in a fairly lengthy defrost cycle.

U.S. Pat. No. 5,673,567, issued on Oct. 7, 1997 to the present inventor, discloses a system wherein hot gas from the compressor discharge line is fed to the refrigerant coil by a valve circuit and back into the liquid manifold to mix with the refrigerant liquid. This method of defrost usually takes about 12 minutes for defrosting evaporators associated with open display cases and about 22 minutes for defrosting frozen food enclosures. The compressors are affected by hot gas coming back through the suction header, thereby causing the compressors to overheat. Furthermore, the energy costs increases with the compressor head pressure increase.

U.S. Pat. No. 6,089,033, published on Jul. 18, 2000 to the present inventor, introduces an evaporator defrost system operating at high speed (e.g., 1 to 2 minutes for refrigerated display cases, 4 to 6 minutes for frozen food enclosures) comprising a defrost conduit circuit connected to the discharge line of the compressors and back to the suction header through an auxiliary reservoir capable of storing the entire refrigerant load of the refrigeration system. The auxiliary reservoir is at low pressure and is automatically flushed into the main reservoir when liquid refrigerant accumulates to a predetermined level. The pressure difference between the low pressure auxiliary reservoir and the typical high pressure of the discharge of the compressor creates a rapid flow of hot gas through the evaporator coils, thereby ensuring a quick defrost of the refrigeration coils. Furthermore, the suction header is fed with low-pressure gas to prevent the adverse effects of hot gas and high head pressure on the compressors.

Such defrost refrigeration systems are efficient in defrosting evaporators. However, new compressor systems are now available, which compressor systems operate differently from existing compressors commonly used in the refrigeration systems. It is therefore desirable to adapt defrost configurations to such new compressor systems so as to optimize the defrost of evaporators.

SUMMARY OF INVENTION

It is therefore an aim of the present invention to provide a novel defrost refrigeration system.

Therefore, in accordance with the present invention, there is provided a defrost refrigeration system of the type having a main refrigeration circuit in which a refrigerant absorbs heat from an evaporator stage and releases heat in a condensation stage, with a compression stage sequentially between the evaporation stage and the condensation stage during a refrigeration cycle, said defrost refrigeration system comprising: at least a first compressor and a second compressor serially positioned with respect to one another such that refrigerant going through the compression stage in the refrigeration cycle passes sequentially through the first compressor and the second compressor; a first line extending from an exit of one of the first compressor and the second compressor of the compression stage, and in fluid communication with the evaporator stage in a defrost cycle and adapted to receive a defrost portion of refrigerant compressed in the compression stage; and valves for switching at least one evaporator between the refrigeration cycle and the defrost cycle, by stopping/allowing a flow of refrigerant from the condensation stage to at least one evaporator of the evaporation stage in the refrigeration cycle, and for allowing/stopping a flow of said defrost portion of refrigerant to defrost the at least one evaporator in the defrost cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof and in which:

FIG. 1 is a block diagram of a defrost refrigeration system constructed in accordance with a preferred embodiment of the present invention;

FIG. 2 is a schematic view of a defrost refrigeration system in accordance with a first embodiment of the present invention;

FIG. 3 is a schematic view of a defrost refrigeration system in accordance with a second embodiment of the present invention; and

FIG. 4 is a schematic view of the defrost refrigeration system of FIG. 3, with an alternative configuration at the exit of refrigeration of a defrost cycle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and more particularly to FIG. 1, a defrost refrigeration system in accordance with a preferred embodiment is generally shown at 10. The defrost refrigeration system 10 operates a refrigeration cycle and has a compression stage 12, a condensation/heat reclaim stage 14 and an evaporation stage 16.

In the refrigeration cycle, the compression stage 12 performs a compression of a refrigerant to a high-pressure gas state. The compression stage 12 is in fluid communication with the condensation/heat reclaim stage 14 by way of line 13.

The condensation/heat reclaim stage 14 releases heat from the high-pressure gas refrigerant received from the compression stage 12. The heat is released to the atmosphere, for instance using roof-top condensers. Alternatively, heat may be recuperated using heat reclaim systems in series or in parallel with condensers. Moreover, the condensation/heat reclaim stage 14 may have refrigerant tanks to accumulate refrigerant having released heat and ready to be fed to the evaporation stage 16.

The condensed refrigerant is directed to the evaporation stage 16 using line 15. The evaporation stage 16 typically has numerous evaporators in refrigeration cabinets, as well as the necessary expansion valves if required to set the refrigerant to a suitable condition to absorb heat. In some instances, the evaporators may be flooded with liquid refrigerant such that expansion valves are optional.

The refrigerant having absorbed heat is then directed to the compression stage 12 using line 18 to complete the refrigeration cycle.

The compression stage 12 uses high-efficiency compressors. More specifically, the compressors used in the compression stage 12 are magnetic-bearing, variable-speed centrifugal compressors of the type manufactured by Turbocor. These compressors operate at high efficiency, but offer a compression ratio at a maximum of 4.5/5:1.

Accordingly, as shown in FIG. 1, these compressors are cascaded in the compression stage 12 of FIG. 1. It is required to cascade the compressors so as to provide the required compression of refrigerant in view of the warmer periods of the year, during which high pressures of refrigerant must be reached for the effective release of heat. More specifically, one or more first compressors 20 compress refrigerant that is fed through line 21 to an accumulator 22. One or more second compressors 24 are positioned downstream of the accumulator 22, and compress refrigerant that is fed from the accumulator 22 through line 23. The refrigerant then exits the compression stage 12 to be fed to the condensation/heat reclaim stage 14.

In order to proceed with the defrost of evaporators from the evaporation stage 16, low pressure refrigerant is directed from the compression stage 12 to the at least one evaporator of the evaporation stage 16.

In a first embodiment, the low-pressure refrigerant is produced by the first compressor 20 and a portion of this refrigerant is fed directly to the evaporator of the evaporation group 16 that is to be defrosted. As the first compressors 20 compress the refrigerant to a relatively low pressure, the refrigerant may be fed directly to the evaporators for defrost. As is shown in FIG. 1, a line 25 directs a portion of refrigerant from the first compressor 20 to the evaporation stage 16 for defrost.

In the first embodiment, the refrigerant that has released heat during defrost is returned to the compression stage 12 for compression. Depending on its condition, the defrost refrigerant uses either the lines 17 or 18, through an appropriate network of valves, to be fed to the first compressor 20 or to the accumulator 22. Moreover, the defrost refrigerant may also be re-injected in the evaporation stage 16 or directed to the condensation/heat reclaim stage 14, depending on its state.

Referring to FIG. 2, the first embodiment of the defrost refrigeration system 10 is illustrated in further details. Like elements bear like reference numerals in the FIGS. 1 to 4. In FIG. 2, the defrost refrigeration system 10′ has a roof-top condenser 14′ and a heat-reclaim loop 14″. The evaporation stage 16 is separated into a group of low-temperature evaporators 16A (e.g., freezer applications), and a group of medium-temperature evaporators 16B (e.g., refrigerator applications). Reference numerals affixed with an A pertain to low-temperature refrigeration in FIGS. 2 to 4, whereas reference numerals affixed with a B will relate to medium-temperature refrigeration in FIGS. 2 to 4. Other evaporators 16C are typically provided in the defrost refrigeration system 10′, but are not illustrated to simplify FIG. 2.

In the first embodiment illustrated in FIG. 1, some refrigerant is directed by the line 25 from the output of the first compressor/compressors 20 to the evaporator stage 16 for defrost. As shown in FIG. 2, the line 25 diverges into lines 25A and 25B to respectively feed the evaporators 16A and 16B, respectively, with defrost refrigerant.

The lines 25A and 25B merge into the return lines 18A and 18B, using appropriate valves to prevent the defrost refrigerant to be sucked by the compressor stage 12. More specifically, valves 30A and 30B are opened while valves 31A and 31B are closed in the defrost sequence. These valves are in opposite positions during a refrigeration cycle.

Defrost refrigerant is therefore directed to the evaporators 16A and/or 16B in a defrost cycle. As is illustrated in FIG. 2, a bypass 32A/32B is provided for the defrost refrigerant to surround the expansion valves of the evaporation stage 16.

The defrost refrigerant having released heat during defrost in the evaporators 16A/16B is then directed to the accumulator 22 using lines 17A/17B, respectively, which merge into line 17. Valves 33A/33B are opened during the defrost cycle, whereas the valves 34A/34B are closed. These valves are in opposite positions during a refrigeration cycle.

In a second embodiment, the low-pressure refrigerant is produced by the second compressor 24 and a portion of this refrigerant is fed to the evaporator of the evaporation group 16 that is to be defrosted. As the first compressors 24 compress the refrigerant to a relatively high pressure, a pressure-reducing device 27 is provided to ensure that the refrigerant fed to defrost evaporators is at a suitable low pressure. As is shown in FIG. 1, a line 26 directs a portion of refrigerant from the second compressor 24 to the evaporation stage 16 for defrost, with the pressure-reducing device 27 being positioned in the line 26.

In the second embodiment, the refrigerant that has released heat during defrost is either returned to the compression stage 12 for compression, or re-injected into the evaporation stage 16 to be used in the refrigeration cycle. Depending on its condition, the defrost refrigerant uses either the lines 17 or 18, through an appropriate network of valves, to be fed to the first compressor 20 or to the accumulator 22.

Referring to FIG. 3, the second embodiment of the defrost refrigeration system is illustrated in further detail. In FIG. 3, the defrost refrigeration system 10″ has stages similar to that of the defrost refrigeration system 10′ of FIG. 2, whereby like elements will bear like reference numerals.

In the second embodiment illustrated in FIG. 1, some refrigerant is directed by the line 26 from the output of the second compressor/compressors 24 to the evaporator stage 16 for defrost, passing through a pressure-reducing device 27 or a suitable solenoid valve. As shown in FIG. 3, the line 26 diverges into lines 26A and 26B to respectively feed the evaporators 16A and 16B, respectively, with defrost refrigerant. Similarly to the defrost refrigeration system 10′ of FIG. 2, the defrost refrigeration system 10″ operates a defrost cycle using the return lines 18A/18B, using a network of valves for the defrost refrigerant to be directed to the evaporators.

During the defrost of the evaporators, the valves 34A and 34B control the flow of defrost refrigerant in the evaporators, by releasing refrigerant into the line 15. During a refrigeration cycle, the valves 34A and 34B are opened.

Referring to FIG. 3, a heat exchanger 40 is provided between the lines 15 and 17′. The line 15 directs refrigerant in the refrigeration cycle from the condensation/heat reclaim stage 14 to the evaporator stage 16. The line 17′ directs refrigerant from the condensation/heat reclaim stage 14 to the accumulator 22, so as to ensure that the refrigerant in the accumulator 22 is in a suitable condition to be fed to the second compressor 24. As such that lines 15 and 17′ converge downstream of the heat exchanger 40. The heat exchanger 40, along with expansion valve 41, controls the conditions of the refrigerant being fed to the evaporator stage 16 for refrigerating purposes and to the accumulator 22.

In an alternative configuration of the second embodiment illustrated in FIG. 4, a defrost refrigeration system is illustrated as 10′″. In FIG. 4, the defrost refrigeration system 10′″ has stages similar to that of the defrost refrigeration system 10′ of FIGS. 2 and 10″ of FIG. 4, whereby like elements will bear like reference numerals.

A portion of refrigerant is directed by the line 26 from the output of the second compressor/compressors 24 to the evaporator stage 16 for defrost, passing through a pressure-reducing device 27 or suitable solenoid valve. As shown in FIG. 4, the line 26 diverges into lines 26A and 26B to respectively feed the evaporators 16A and 16B, respectively, with defrost refrigerant. Similarly to the defrost refrigeration system 10′ of FIGS. 2 and 10″ of FIG. 3, the defrost refrigeration system 10′″ operates a defrost cycle using the return lines 18A/18B, using a network of valves for the defrost refrigerant to be directed to the evaporators. The defrost refrigerant is then directed to the accumulator 22 at the compression stage 12 using line 17.

The lines 25A and 25B merge into the return lines 18A and 18B, using appropriate valves to prevent the defrost refrigerant to be sucked by the compressor stage 12. More specifically, valves 30A and 30B are opened while valves 31A and 31B are closed in the defrost sequence. These valves are in opposite positions during a refrigeration cycle.

Defrost refrigerant is therefore directed to the evaporators 16A and/or 16B in a defrost cycle. As is illustrated in FIG. 4, a bypass 32A/32B is provided for the defrost refrigerant to surround the expansion valves of the evaporation stage 16.

The defrost refrigerant having released heat during defrost in the evaporators 16A/16B is then directed to the accumulator 22 using lines 17A/17B, respectively, which merge into line 17. Valves 33A/33B are opened during the defrost cycle, whereas the valves 34A/34B are closed. These valves are in opposite positions during a refrigeration cycle.

Although the choice of refrigerants has not been described, it is pointed out that any suitable refrigerant can be used taking into account the conditions at which the refrigeration system will operate. 

1. A defrost refrigeration system of the type having a main refrigeration circuit in which a refrigerant absorbs heat from an evaporator stage and releases heat in a condensation stage, with a compression stage sequentially between the evaporation stage and the condensation stage during a refrigeration cycle, said defrost refrigeration system comprising: at least a first compressor and a second compressor serially positioned with respect to one another such that refrigerant going through the compression stage in the refrigeration cycle passes sequentially through the first compressor and the second compressor; a first line extending from an exit of one of the first compressor and the second compressor of the compression stage, and in fluid communication with the evaporator stage in a defrost cycle and adapted to receive a defrost portion of refrigerant compressed in the compression stage; and valves for switching at least one evaporator between the refrigeration cycle and the defrost cycle, by stopping/allowing a flow of refrigerant from the condensation stage to at least one evaporator of the evaporation stage in the refrigeration cycle, and for allowing/stopping a flow of said defrost portion of refrigerant to defrost the at least one evaporator in the defrost cycle.
 2. The defrost refrigeration system according to claim 1, wherein the first line is positioned at the exit of the first compressor and is in fluid communication with the evaporation stage during the defrost cycle.
 3. The defrost refrigeration system according to claim 2, further comprising a second line in fluid communication between the evaporation stage and the compression stage during the defrost cycle, and valves for directing the defrost portion of refrigerant to the compression stage after defrost.
 4. The defrost refrigeration system according to claim 1, wherein the first line is positioned at the exit of the second compressor and is in fluid communication with the evaporation stage during the defrost cycle.
 5. The defrost refrigeration system according to claim 4, further comprising a pressure-reducing device on the first line for reducing a pressure of said defrost portion of refrigerant for subsequent defrost of the at least one evaporator.
 6. The defrost refrigeration system according to claim 4, further comprising a second line in fluid communication between the evaporation stage and the compression stage during the defrost cycle, and valves for directing the defrost portion of refrigerant to the compression stage after defrost.
 7. The defrost refrigeration system according to claim 4, wherein the defrost portion of refrigerant is directed to the evaporation stage after defrost to mix with refrigerant from the condensation stage to feed evaporators in the refrigeration cycle. 